Multi-chip module with a high-rate interface

ABSTRACT

A multi-chip module (MCM) may include a substrate, and first and second physical-layer (PHY) chips mounted on the substrate. In some implementations, the first PHY chip includes a multiplexer and a PHY circuit. The multiplexer is configured to receive a multiplexed data stream from a media access control (MAC) device, to demultiplex the multiplexed data stream into first and second data streams, to output the first data stream to the PHY circuit, and to output the second data stream to the second PHY chip. In some implementations, the first PHY includes a router and a PHY circuit. The router is configured to receive a plurality of data packets from a MAC device, to route one or more of the data packets having a first address to the PHY circuit, and to route one or more of the data packets having a second address to the second PHY chip.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/648,227, entitled “Method for Implementing a Multi-Chip Module With aHigh-Rate Interface,” filed on Oct. 9, 2012, which is expresslyincorporated by reference herein.

TECHNICAL FIELD

The present description relates generally to multi-chip modules, andmore particularly, to multi-chip modules with a high-rate interface.

BACKGROUND

Ethernet is widely used to transport voice, data and multimedia trafficbetween computing devices because of its high speed, relatively lowcost, and ease of installation. A computing device (e.g., a voice overInternet (VoIP) device, a network camera, a computer, etc.) may beconnected to an Ethernet switch or an access point by an Ethernet cable,and may communicate with another computing device via the Ethernetswitch or access point.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of the subject technology are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of thesubject technology are set forth in the following figures.

FIG. 1 illustrates an example of an Ethernet system that includes asingle-port physical layer (PHY) chip.

FIG. 2 illustrates an example of an Ethernet system that includes amulti-port physical layer (PHY) chip.

FIG. 3 illustrates an example multi-chip module with a high-rateinterface according to some aspects of the subject technology.

FIG. 4 illustrates an example single-port Ethernet system according tosome aspects of the subject technology.

FIG. 5 illustrates an example programmable multiplexer according to someaspects of the subject technology.

FIG. 6 illustrates an example media access control (MAC) deviceaccording to some aspects of the subject technology.

FIG. 7 illustrates an example multi-chip module with multiple interfacesaccording to some aspects of the subject technology.

FIG. 8 illustrates an example programmable multiplexer according to someaspects of the subject technology.

FIG. 9 illustrates a multi-chip module according to some aspects of thesubject technology.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofvarious configurations of the subject technology and is not intended torepresent the only configurations in which the subject technology may bepracticed. The appended drawings are incorporated herein and constitutea part of the detailed description. The detailed description includesspecific details for the purpose of providing a thorough understandingof the subject technology. However, the subject technology is notlimited to the specific details set forth herein and may be practicedwithout one or more of the specific details. In some instances,structures and components are shown in block diagram form in order toavoid obscuring the concepts of the subject technology.

FIG. 1 shows an example of an Ethernet system 100 that may be used in anaccess point to provide a computing device with access to an Ethernetnetwork. The Ethernet system 100 includes a media access control (MAC)device 105, a single-port physical layer device (PHY) 110, and aconnector 130 (e.g., RJ-45 connector) that connects the Ethernet system100 to an Ethernet cable (not shown). The Ethernet cable may includewires (e.g., copper wires) or optical fibers. In some implementations,the Ethernet cable includes four twisted wire pairs.

The MAC device 105 implements data-link layer (OSI layer 2) processingof data, including encapsulation of data into frames and media accessmanagement. The MAC device 105 outputs a data stream to the PHY 110 viaa MAC/PHY interface 115 (e.g., a serial gigabit media independentinterface (SGMII)). The PHY 110 may perform physical-layer (OSI layer 1)processing on the data stream from the MAC device 105 to convert thedata stream into a physical-layer data signal for transmission on theEthernet cable. The physical layer may include a physical codingsublayer and a physical medium dependent sublayer. The physical-layerdata signal from the PHY 110 is output to the Ethernet cable via theconnector 130.

FIG. 2 shows an example of an Ethernet system 200 that may be used in amulti-port Ethernet switch to connect multiple devices to an Ethernetnetwork. The Ethernet system 200 includes a MAC device 205, a quad-portPHY 210, and four connectors 230A-230D (e.g., four RJ-45 connectors)that connect the Ethernet system 200 to four separate Ethernet cables(not shown).

The MAC device 205 implements data-link layer (OSI layer 2) processingof data, including encapsulation of data into frames and media accessmanagement. The MAC device 205 may receive data to be transmitted on thefour Ethernet cables to different computing devices, and process thedata at the data-link layer into four data streams, where each datastream is to be transmitted on a different one of the Ethernet cables.The MAC device 205 may multiplex the data streams into a multiplexeddata stream (e.g., a serial multiplexed data stream), and output themultiplexed data stream to the quad-port PHY 210 via a MAC/PHY interface215 (e.g., a quad SGMII (QSGMII)). For QSGMII implementations, each datastream may have a data rate of approximately 1 Gbit/s and themultiplexed data stream may have a data rate of approximately 4 Gbit/s.

The quad-port PHY 210 includes a multiplexer (MUX) 220, and fourphysical layer (PHY) circuits 225A-225D. The MUX 220 demultiplexes themultiplexed data stream from the MAC device 205 into the four datastreams. For QSGMII implementations, the MUX 220 may demultiplex aQSGMII data stream into four SGMII data streams. The MUX 220 outputseach data stream to a different one of the PHY circuits 225A-225D. EachPHY circuit 225A-225D performs physical-layer (OSI layer 1) processingon the respective data stream to convert the data stream into aphysical-layer data signal for transmission on the respective Ethernetcable. Each PHY circuit 225A-225D outputs the respective physical-layerdata signal to the respective Ethernet cable via the respectiveconnector 230A-230D (e.g., RJ-45 connector).

The quad-port PHY 210 may be integrated on a single chip. An advantageof integrating the quad-port PHY 210 is that it reduces the number ofoff-chip I/Os in an Ethernet switch. This is because the quad-port PHY210 uses a single high-speed MAC/PHY interface to communicate with theMAC device 205.

To address both the single-port market (e.g., access point market) andthe multi-port market (e.g., Ethernet switch market), a PHY chipmanufacturer may separately develop a single-port PHY chip and amulti-port PHY chip (e.g., a quad-port PHY chip). However, havingseparate chip developments to address both markets drives up developmentcosts. Accordingly, it is desirable to develop a PHY chip that canaddress both markets.

FIG. 3 illustrates an example multi-port system 300 including amulti-chip module (MCM) 312 according to aspects of the subjecttechnology. The MCM 312 includes a first single-port PHY 310A, a secondsingle-port PHY 310B, a third single-port PHY 310C, and a fourthsingle-port PHY 310D. Each single-port PHY 310A-310D may be integratedon a separate chip or die, and may be identical. The single-port PHYs310A-310D may be mounted on a common substrate 315, such as a ceramicsubstrate, and/or another type of substrate to form the MCM 312.

Each single-port PHY 310A-310D includes a MUX 320A-320D and a PHYcircuit 325A-325D for performing physical-link layer processing. Eachsingle-port PHY 310A-310D is connected to a respective Ethernet cable(not shown) via a respective connector 330A-330D (e.g., RJ-45connector). The first single-port PHY 320A is connected to the MACdevice 205 via a high-speed MAC/PHY interface 215. In addition, thefirst single-port PHY 320A is connected to the second, third and fourthsingle-port PHYs 310B, 310C and 310D via lower-speed interfaces 324, 326and 328, respectively, as shown in FIG. 3. The interfaces 324, 326 and328 interconnect the PHYs 310A-310D of the MCM 312. Any of thelower-speed interfaces 324, 326 and 328 may include a conductive traceon the substrate 315.

In operation, the MAC device 205 receives data to be transmitted on thefour Ethernet cables, processes the data at the data-link layer intofour data streams, and multiplexes the data streams into a multiplexeddata stream (e.g., a serial multiplexed data stream). The multiplexeddata stream is output to the first single-port PHY 310A via the MAC/PHYinterface 215. The MAC device 205 may multiplex the data streams byinterleaving the bits or bytes of the data streams. The MAC device 205may use another multiplexing technique, including, but to limited to,frequency division multiplexing, code division multiplexing, etc.

The MUX 320A of the first single-port PHY 310A demultiplexes themultiplexed data stream into the four data streams. Each demultiplexeddata stream may have a data rate equal to one-fourth the data rate ofthe multiplexed data stream. The MUX 320A outputs one of the datastreams to the respective PHY circuit 325A on the same chip. The PHYcircuit 325A performs physical-layer (OSI layer 1) processing on thedata stream to convert the data stream into a physical-layer data signalfor transmission on the respective Ethernet cable via connector 330A.

The MUX 320A of the first single-port PHY 310A outputs each of the otherthree data streams to a different one of the second, third and fourthsingle-port PHYs 310B-310D via the respective interface 324, 326 and328. The MUX 320B-320D in each of the second, third and fourthsingle-port PHYs 310B-310D passes the received data stream to therespective PHY circuit 325B-325D. Each PHY circuit 325B-325D performsphysical-layer (OSI layer 1) processing on the respective data stream toconvert the data stream into a physical-layer data signal fortransmission on the respective Ethernet cable via the respectiveconnector 330B-330D.

The single-port PHY that receives the multiplexed data stream from theMAC device 205, demultiplexes the multiplexed data stream, and outputsthe demutiplexed data streams to other PHYs in the MCM 312 may bereferred to as a master PHY. Each of the other single-port PHYs thatreceives a data stream from the master PHY may be referred to as a slavePHY. In the example in FIG. 3, the first single-port PHY 310A acts as amaster PHY and the second, third and fourth single-port PHYs 310B-310Dact as slave PHYs.

The MUX 320A-320D in each of the single-ports PHY 310A-310D may have thecapability of demultiplexing a multiplexed data stream from the MACdevice 205 into demultiplexed data streams. When a single-port PHY actsas a slave, this capability of the respective MUX may be unused, inwhich case the respective MUX may simply pass a received data stream tothe respective PHY circuit.

Any of the MUXs 320A-320D may be implemented using a programmable MUXthat can be selectively programmed to operate in one of a first mode anda second mode. In the first mode, the MUX demultiplexs a multiplexeddata stream from the MAC device 205 into multiple data streams, and, inthe second mode, the MUX passes a received data stream to the respectivePHY circuit. The MUX may be programmed in operate in the first mode orthe second mode depending on whether the respective single-port PHY isto be used as a master or a slave.

Thus, each of the single-port PHYs 310A-310D may be capable of acting asa master PHY or a slave PHY. When a single-port PHY acts as a slave PHY,three of the I/Os of the respective MUX are not used since they are notneeded to output demultiplexed data streams to the other PHYs. As shownin the example in FIG. 3, three of the I/Os 322B of the secondsingle-port PHY 310B are unused, three of the I/Os 322C of the thirdsingle-port PHY 310C are unused, and three of the I/Os 322D of thefourth single-port PHY 310D are unused. All three of the correspondingI/Os 322A of the first single-port PHY 310A are used to outputdemultiplexed data streams to the other singe-port PHYs.

Thus, the subject technology allows a multi-port MCM 312 with oneinterface to the MAC device 205 to be created using multiple single-portPHYs 310A-310D, each of which can be on a separate chip. In addition,any of the single-port PHYs 310A-310D may be used in a single-portsystem (e.g., access point).

FIG. 4 shows an example in which the first single-port PHY 310A is usedin a single-port Ethernet system 400 (e.g., an access point). In thisexample, the MUX 320A of the first single-port PHY 310A may receive adata stream from a MAC device 405 via a MAC/PHY interface 415, and passthe received data stream to the respective PHY circuit 325A forphysical-layer processing. In this case, the demultiplexing function ofthe MUX 320A is not used, and three of the I/Os 322A of the MUX 320A arenot used.

Therefore, the subject technology allows one type of chip to be used inmulti-port and single-port applications. In other words, the subjecttechnology allows one chip development to address both the multi-portmarket (e.g., Ethernet switch) and single-port market (e.g., accesspoint) markets, thereby reducing development costs.

Although the MCM 312 is described above using the example of foursingle-port PHYs, it is to be appreciated that the subject technology isnot limit to this example, and that the MCM 312 may include any numberof single-port PHYs. Generally speaking, the MCM 312 may include Nsingle-port PHYs, in which N is an integer and the MAC device 205multiplexes N data streams into a multiplexed data stream. The MUX in afirst one of the single-port PHYs may demultiplex the multiplexed datastream into the N data streams, output one of the N data streams to therespective PHY circuit for physical-layer processing, and output each ofthe other data streams to a different one of the other single-port PHYs.

FIG. 5 illustrates a programmable MUX 520 according to some aspects ofthe subject technology. The programmable MUX 520 may be used toimplement any one of the MUXs 320A-320D. The programmable MUX 520 may becoupled to four I/Os 522-1 to 522-4 of the respective single-port PHY.I/Os 522-1 and 522-4 may couple the MUX 520 to separate external pins orcontacts (not shown) of the respective single-port PHY for connection toother single-port PHYs and/or a MAC device.

The programmable MUX 520 includes a multiplexer 530, a connection 535 tothe respective PHY circuit, and a switch 532 connected between I/O 522-1and the PHY circuit. The multiplexer 530 may be configured to receive amultiplexed data stream on I/O 522-1, demultiplex the multiplexed datastream into four data streams, output one of the demultiplxed datastreams to the respective PHY circuit via connection 535, and outputeach of the other demultiplexed data streams to a different one of I/Os522-2 to 522-4.

The programmable MUX 520 may be selectively programmed to operate in oneof a first mode and a second mode. In the first mode, the MUX 520demultiplexes a multiplexed data stream. The MUX 520 may be programmedto operate in the first mode by opening switch 532 and powering on themultiplexer 530. When the MUX 520 is to operate in the first mode, I/O522-1 may be connected to the MAC device 205 via a MAC/PHY interface215, and each of I/Os 522-2 to 522-4 may be connected to a different oneof the other single-port PHYs on the MCM 312.

In the first mode, the multiplexer 530 receives a multiplexed datastream from the MAC device 205 via I/O 522-1, demultiplexes themultiplexed data stream, outputs one of the demultiplxed data streams tothe respective PHY circuit via connection 535, and outputs each of theother demultiplexed data streams to a different one of the othersingle-port PHYs via the respective I/O 522-2 to 522-4.

In the second mode, the MUX 520 passes a received data stream to therespective PHY circuit. The MUX 520 may be programmed to operate in thesecond mode by closing switch 532 and powering off the multiplexer 530.Closing the switch 532 creates a path 540 between I/O 522-1 and therespective PHY circuit, bypassing the multiplexer 530. When the MUX 520is to operate in the second mode, I/O 522-1 may be connected to a mastersingle-port PHY or a MAC device. In the second mode, the MUX 520receives a data stream on I/O 522-1 from a master PHY or a MAC device,and passes the received data stream to the respective PHY circuit viapath 540 and connection 535.

FIG. 6 illustrates a MAC device 605 that may be used with the MCM 312according to aspects of the subject technology. The MAC device 605includes four MAC circuits 610A-610D and a multiplexer (MUX) 612. EachMAC circuit 610A-610D performs data-link layer (OSI layer 2) processingon data to be transmitted on a different one of the Ethernet cables, andoutputs a data stream to the MUX 612. The MUX 612 multiplexes the datastreams from the MAC circuits 610A-610D into a multiplexed data stream,and outputs the multiplexed data stream to the MCM 312 via a MAC/PHYinterface 615.

At the MCM 312 (shown in FIG. 3), the MUX 320A of the first single-portPHY 310A demultiplexes the multiplex data stream into the four datastreams corresponding to MAC circuits 610A-610D. The MUX 320A of thefirst single-port PHY 310A outputs the data stream corresponding to MACcircuit 610A to the respective PHY circuit 325A for physical-layerprocessing, and outputs the data streams corresponding to MAC circuits610B, 610C and 610D to the second, third and fourth single-port PHYs610B, 610C and 610D, respectively. Each single-port PHY performsphysical-layer (OSI layer 1) processing on the respective data stream.

In some implementations, the MUX 612 may multiplex the data streams fromMAC circuits 610A-610D using bit-interleaved multiplexing orbyte-interleaved multiplexing. In bit-interleaved multiplexing, the MUX612 interleaves the bits of the data streams, in which the bits of aparticular data stream appear in every fourth bit of the multiplexeddata stream. The MUX 612 may do this by sequentially outputting a firstbit from each data stream, then sequentially outputting a second bitfrom each data stream, and so forth. The MUX 320A of the firstsingle-port PHY 310A may demultiplex the multiplexed data stream byde-interleaving the bits of the multiplexed data stream into the fourdata streams. For example, the MUX 320A may output a demultiplexed datastream at one of the outputs of the MUX 320A by outputting every fourthbit in the multiplexed data stream to that output.

In byte-interleaved multiplexing, the MUX 612 interleaves the bytes ofthe data streams, in which the bytes of a particular data stream appearin every fourth byte of the multiplexed data stream. Each byte may bemade up of 8 bits, 10 bits or another number of bits. The MUX 612 may dothis by sequentially outputting a first byte from each data stream, thensequentially outputting a second byte from each data stream, and soforth. The MUX 320A of the first single-port PHY 310A may demultiplexthe multiplexed data stream by de-interleaving the bytes of themultiplexed data stream into the four data streams. For example, the MUX320A may output a demultiplexed data stream at one of the outputs of theMUX 320A by outputting every fourth byte in the multiplexed data streamto that output.

Although the MAC device 605 is described above using the example of fourMAC circuits 610A-610D, it is to be appreciated that the subjecttechnology is not limit to this example, and that the MAC device 605 mayinclude any number of MAC circuits. Generally speaking, the MAC device605 may include N MAC circuits that output N data streams, in which N isan integer and the MUX 612 multiplexes the N data streams into amultiplexed data stream.

In some implementations, each PHY circuit 325A-325D may output data tothe respective Ethernet cable at a data rate of approximately 2.5Gbit/s. Each PHY circuit 325A-325D may achieve a data rate ofapproximately 2.5 Gbit/s by modulating data using double square (DSQ)128 modulation or other high-level modulation scheme. Any of theEthernet cables may be a CAT 5e cable, a CAT 6 cable, or another type ofcable.

In these implementations, the MAC device 205 may output the multiplexeddata stream at a data rate of approximately 10 Gbit/s, and the MUX 320Aof the first single-port PHY 310A may demultiplex the multiplexed datastream into four data streams, where each data stream has a data rate ofapproximately 2.5 Gbit/s. The MUX 320 may output one of the data streamsto the respective PHY circuit 325A, and output each of the other threedata streams to a different one of the second, third and fourthsingle-port PHYs 310B-310D via the respective interface 324, 326 and328.

Although aspects of the subject technology aspects are described usingthe example in which the single-port PHYs 310A-310D transmit data on therespective Ethernet cables, it is to be appreciated that the single-portPHYs 310A-310D may also receive data from the respective Ethernetcables. Thus, the single-port PHYs 310A-310D may be bi-directional. Insome implementations, when a PHY circuit receives a physical-layer datasignal from the respective Ethernet cable, the PHY circuit may performphysical layer (OSI layer 1) processing on the received physical-layerdata signal to convert the physical-layer data signal into a datastream. The MUX 320B-320D in each of the second, third and fourthsingle-port PHYs 310B-310D may output the respective data stream to theMUX 320A of the first single-port PHY 310A via the respective interface324, 326 and 328. The MUX 320A in the first single-port PHY 310A maymultiplex the data stream from the respective PHY circuit 325A with thedata streams from the other single-port PHYs 310B-310D into amultiplexed data stream, and output the multiplexed data stream to theMAC device 205 via the MAC/PHY interface 215.

The MCM 312 may also be connected to multiple MAC devices via multipleMAC/PHY interfaces. In this regard, FIG. 7 shows an example multi-portsystem 700 including four MAC devices 705A-705D connected to thesingle-port PHYs 310A-310D of the MCM 312 via separate MAC/PHYinterfaces 715A-715D, respectively. Each MUX 320A-320D receives a datastream from the respective MAC device 705A-705D via the respectiveMAC/PHY interface 715A-715D, and passes the received data stream to therespective PHY circuit 325A-325D for physical-layer processing. In thiscase, the interfaces 324, 326 and 328 connecting the first single-portPHY 310A to the second, third and fourth single-port PHYs 310B-310D,respectively, are not used.

Each MUX 320A-320D may be implemented using a programmable MUX that canbe programmed to pass a data stream received on any I/O of the MUX tothe respective PHY circuit for physical-layer processing. For example,when the MCM 312 is used in the multi-port system 700 in FIG. 7, the MUX320A-320D is each single-port PHY 310A-310D may be programmed to pass adata stream received on the I/O connected to the respective MAC/PHYinterface 715A-715D to the respective PHY circuit 325A-325D. In thiscase, each single-port PHYs 310A-310D may operate independently, and theelectrical interconnections (i.e., interfaces 324, 326 and 328) betweenthe single-port PHYs 310A-310D are not used.

When the MCM 312 is used in the multi-port system 300 in FIG. 3, the MUX320A in the first single-port PHY 310A may be programmed to demultiplexa multiplex data stream received on the I/O connected to the MAC/PHYinterface 215, output one of the demultiplexed data streams to therespective PHY circuit 325A, and output each of the other demultiplexeddata streams to a different one of the three I/Os connected to theinterfaces 324, 326 and 328. The MUX 320B-320D in each of the second,third and fourth single-port PHYs 310B-310D may be programmed to pass adata stream received on the I/O connected to the respective interface324, 326 and 328 to the respective PHY circuit 325B-325D.

Thus, the MCM 312 may be connected to a MAC device 205 via a singlehigh-rate MAC/PHY interface or connected to multiple MAC devices705A-705D via separate lower-rate MAC/PHY interfaces 715A-715D. Thisprovides the MCM 312 with the flexibility of being used in differentsystem configurations.

FIG. 8 illustrates a programmable MUX 820 according to some aspects ofthe subject technology. The programmable MUX 820 is similar to theprogrammable MUX 520 in FIG. 5, and further includes a second switch 832connected between I/O 522-2 and connection 535 to the respective PHYcircuit.

When the programmable MUX 820 is used to demultiplex a multiplexed datastream from the MAC device 205 or pass a data stream received on I/O522-1 to the respective PHY circuit, the second switch 832 may be open.When the programmable MUX 820 is used to pass a data stream receivedfrom the respective MAC device 705A-705D in the system 700 in FIG. 7,I/O 522-2 may be connected to the respective MAC device 705A-705D viathe respective MAC/PHY interface 715A-715D, the second switch 832 may beclosed, the first switch 532 may be open, and the multiplexer 530 may bepowered off. In this case, closing the second switch 832 creates a path840 between I/O 522-2 and the respective PHY circuit that bypasses themultiplexer 530. As a result, a data stream received from the respectiveMAC device on I/O 522-2 is passed to the respective PHY circuit.

FIG. 9 illustrates an example multi-port system 900 including amulti-chip module (MCM) 912 according to aspects of the subjecttechnology. The MCM 912 includes a first single-port PHY 910A, a secondsingle-port PHY 910B, a third single-port PHY 910C, and a fourthsingle-port PHY 910D. Each single-port PHY 910A-910D may be integratedon a separate chip or die, and may be identical. The single-port PHYs910A-910D may be mounted on a common substrate 914 to form the MCM 912.

Each single-port PHY 910A-910D includes a packet router 920A-920D and aPHY circuit 925A-925D for performing physical-link layer processing.Each single-port PHY 910A-910D is connected to a respective Ethernetcable (not shown) via a respective connector 930A-930D (e.g., RJ-45connector). The first single-port PHY 920A is connected to the MACdevice 905 via a high-speed MAC/PHY interface 915. In addition, thefirst single-port PHY 320A is connected to the second, third and fourthsingle-port PHYs 910B, 910C and 910D via lower-speed interfaces 924, 926and 928, respectively, as shown in FIG. 9.

In operation, the MAC device 905 receives data to be transmitted on thefour Ethernet cables to four different computing devices (e.g., VoIPdevices, access points, etc.). The MAC device 905 processes the data foreach computing device into data packets, where each packet may includean address identifying the computing device as a destination of thepacket. A data packet may also be referred to as a frame. The MAC device905 outputs the data packets for the different computing devices to theMCM 912 via the interface 915. The MAC device 905 may output the datapackets for the different computing devices one packet at a time. Forexample, the MAC device 905 may interleave the data packets for thedifferent computing devices and output the interleaved packets to theMCM 912 via the interface 915.

In some implementations, the data packets for the different computingdevices may have different sizes. In these implementations, the MACdevice 905 may manage the data packet traffic such that the data rate(number of bits per unit of time) for each computing device isapproximately the same. In other words, the MAC device 905 may implementa traffic policy in which each computing device (and hence respectivePHY) is allocated approximately an equal share of the total data rate ofthe interface 915.

To do this, the MAC device 905 may include a buffer that temporarilystores data packets for the different computing devices. The MAC device905 may then output the data packets in the buffer to the interface 915in an order that results in approximately equal data rates for thecomputing devices. For example, if large data packets are addressed to afirst one of the computing devices and smaller packets are addressed toa second one of the computing devices, then the MAC device 905 mayoutput several packets addressed to the second computing device forevery packet addressed to the first device such that the data rates forthe devices are approximately equal. For implementations in which eachsingle-port PHY 910A-910D operates at a data rate of approximately 2.5Gbits/s, the MAC device 905 may manage the data packet traffic such thatthe data rate for each computing device is approximately 2.5 Gbits/s. Inthis case, the data rate of the interface 915 may be 10 Gbits/s.

The router 920A of the first single-port PHY 910A looks at the addressesof incoming data packets from the MAC device 905, and routes the datapackets accordingly. If a packet is addressed to a computing devicecorresponding to the first single-port PHY 910A, the router 920A routesthe data packet to the respective PHY circuit 925A for physical-layerprocessing. If a packet is addressed to a computing device correspondingto the second single-port PHY 910B, the router 920A routes the datapacket to the second single-port PHY 910B via the respective interface924. If a packet is addressed to a computing device corresponding to thethird single-port PHY 910C, the router 920A routes the data packet tothe third single-port PHY 910C via the respective interface 926. If apacket is addressed to a computing device corresponding to the fourthsingle-port PHY 910D, the router 920A routes the data packet to thefourth single-port PHY 910D via the respective interface 928.

The router 920B-920D in each of the second, third and fourth single-portPHYs 910B-910D passes received packets to the respective PHY circuit925B-925D. Each PHY circuit 925B-925D performs physical-layer (OSIlayer 1) processing on the respective data packets to convert the datapackets into a physical-layer data signal for transmission to therespective computing device via the respective Ethernet cable.

The router 920A-920D in each of the single-port PHYs 910A-910D may havethe capability of routing each data packet from the MAC device 905 tothe respective PHY circuit or another single-port PHY based on theaddress of the packet. When a single-port PHY 910A-910D acts as a slave,the address routing functionality of the respective router may be turnedoff, in which case the respective router may simply pass a received datapacket to the respective PHY circuit without looking at the address ofthe packet.

In some implementations, each router 920A-920D may be configured to beselectively programmed to operate in one of a first mode and a secondmode. In the first mode, the router may be configured to route datapackets based on addresses of the data packets. For example, the routermay route packets addressed to a computing device corresponding to thecorresponding single-port PHY to the respective PHY circuit, and routepackets addressed to other computing devices to the correspondingsingle-port PHYs. In the second mode, the router may be configured topass data packets received from a master PHY or a MAC device to therespective PHY without looking at the addresses of the packets.

Thus, each of the single-port PHYs 910A-910D may be capable of acting asa master PHY or a slave PHY. When a single-port PHY acts as a slave PHY,three of the I/Os of the respective router are not used since they arenot needed to route packets to the other PHYs. As shown in the examplein FIG. 9, three of the I/Os 922B of the second single-port PHY 910B areunused, three of the I/Os 922C of the third single-port PHY 910C areunused, and three of the I/Os 922D of the fourth single-port PHY 910Dare unused. All three of the corresponding I/Os 922A of the firstsingle-port PHY 910A are used to route packets to the other singe-portPHYs.

The functions described above can be implemented in digital electroniccircuitry, in computer software, firmware or hardware. The techniquescan be implemented using one or more computer program products.Programmable processors and computers can be included in or packaged asmobile devices. The processes and logic flows can be performed by one ormore programmable processors and by one or more programmable logiccircuitry.

Some implementations can include electronic components, such asmicroprocessors, storage and memory that store computer programinstructions in a machine-readable or computer-readable medium(alternatively referred to as computer-readable storage media,machine-readable media, or machine-readable storage media). Someexamples of such computer-readable media include RAM, ROM, read-onlycompact discs (CD-ROM), recordable compact discs (CD-R), rewritablecompact discs (CD-RW), read-only digital versatile discs (e.g., DVD-ROM,dual-layer DVD-ROM), a variety of recordable/rewritable DVDs (e.g.,DVD-RAM, DVD-RW, DVD+RW, etc.), flash memory (e.g., SD cards, mini-SDcards, micro-SD cards, etc.), magnetic and/or solid state hard drives,ultra density optical discs, any other optical or magnetic media, andfloppy disks. The computer-readable media can store a computer programthat is executable by at least one processing unit and includes sets ofinstructions for performing various operations. Examples of computerprograms or computer code include machine code, such as is produced by acompiler, and files including higher-level code that are executed by acomputer, an electronic component, or a microprocessor using aninterpreter.

Some implementations can be performed by a microprocessor or multi-coreprocessors that execute software. Some implementations can be performedby one or more integrated circuits, such as application specificintegrated circuits (ASICs) or field programmable gate arrays (FPGAs).In some implementations, such integrated circuits can executeinstructions that are stored on the circuit itself.

Many of the above-described features and applications may be implementedas software processes that are specified as a set of instructionsrecorded on a computer readable storage medium (also referred to ascomputer readable medium). When these instructions are executed by oneor more processing unit(s) (e.g., one or more processors, cores ofprocessors, or other processing units), they cause the processingunit(s) to perform the actions indicated in the instructions. Examplesof computer readable media include, but are not limited to, CD-ROMs,flash drives, RAM chips, hard drives, EPROMs, etc. The computer readablemedia does not include carrier waves and electronic signals passingwirelessly or over wired connections.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but are to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. Pronouns in themasculine (e.g., his) include the feminine and neuter gender (e.g., herand its) and vice versa. Headings and subheadings, if any, are used forconvenience only and do not limit the subject disclosure.

The predicate words “configured to”, “operable to”, and “programmed to”do not imply any particular tangible or intangible modification of asubject, but, rather, are intended to be used interchangeably. Forexample, a processor configured to monitor and control an operation or acomponent may also mean the processor being programmed to monitor andcontrol the operation or the processor being operable to monitor andcontrol the operation. Likewise, a processor configured to execute codecan be construed as a processor programmed to execute code or operableto execute code.

A phrase such as an “aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations, or one or more configurations. Aphrase such as an aspect may refer to one or more aspects and viceversa. A phrase such as a “configuration” does not imply that suchconfiguration is essential to the subject technology or that suchconfiguration applies to all configurations of the subject technology. Adisclosure relating to a configuration may apply to all configurations,or one or more configurations. A phrase such as a configuration mayrefer to one or more configurations and vice versa.

The word “example” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “example” is notnecessarily to be construed as preferred or advantageous over otheraspects or designs.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. §112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor.” Furthermore, to the extent that the term “include,” “have,” or thelike is used in the description or the claims, such term is intended tobe inclusive in a manner similar to the term “comprise” as “comprise” isinterpreted when employed as a transitional word in a claim.

What is claimed is:
 1. A multi-chip module, comprising: a firstphysical-layer (PHY) chip comprising a first PHY circuit; a second PHYchip; and a first low-speed physical interface coupling the first PHYchip to the second PHY chip; wherein the first PHY chip is configured toreceive a data stream from a media access control (MAC) device over ahigh-speed physical interface, the data stream comprising first dataassociated with the first PHY chip and second data associated with thesecond PHY chip, to extract the first data and the second data from thedata stream, to output the first data to the first PHY circuit of thefirst PHY chip, and to output the second data to the second PHY chip viathe first low-speed physical interface.
 2. The multi-chip module ofclaim 1, wherein the low-speed physical interface provides datatransmission at a lower data rate than the high-speed physicalinterface.
 3. The multi-chip module of claim 1, wherein the first PHYchip further comprises a first multiplexer that is configured todemultiplex the data stream to extract the first data and the seconddata.
 4. The multi-chip module of claim 3, further comprising: a thirdPHY chip; a fourth PHY chip; a second low-speed physical interfacecoupling the first PHY chip to the third PHY chip; and a third low-speedphysical interface coupling the first PHY chip to the fourth PHY chip;wherein the data stream further comprises third data associated with thethird PHY chip and fourth data associated with the fourth PHY chip, andthe first PHY chip is further configured to extract the third data andthe fourth data from the data stream, to output the third data to thethird PHY chip via the second low-speed physical interface, and tooutput the fourth data to the fourth PHY chip via the third low-speedphysical interface.
 5. The multi-chip module of claim 4, wherein thefirst, second, and third low-speed physical interfaces are configuredfor data transmission at approximately one-fourth the data rate of thehigh-speed physical interface.
 6. The multi-chip module of claim 5,wherein the high-speed physical interface is configured for datatransmission at approximately 10 Gbits per second, and the first,second, and third low-speed physical interfaces are configured for datatransmission at approximately 2.5 Gbits per second.
 7. The multi-chipmodule of claim 3, wherein the second PHY chip comprises a secondmultiplexer and a second PHY circuit, and wherein the second multiplexeris configured to receive the second data from the first PHY chip via thefirst physical interface, and to pass the second data to the second PHYcircuit.
 8. The multi-chip module of claim 7, wherein the secondmultiplexer is configured to selectively operate in one of a first modeand a second mode, in the first mode, the second multiplexer isconfigured to demultiplex a multiplexed data stream, in the second mode,the second multiplexer is configured to pass the second data to thesecond PHY circuit, and the second multiplexer is programmed to operatein the second mode.
 9. The multi-chip module of claim 8, wherein thefirst PHY chip and the second PHY chip are substantially identical. 10.The multi-chip module of claim 7, wherein the first PHY circuit isconfigured to convert the first data into a first physical-layer datasignal for transmission on a first Ethernet cable, and the second PHYcircuit is configured to convert the second data into a secondphysical-layer data signal for transmission on a second Ethernet cable.11. The multi-chip module of claim 1, wherein the first PHY chip and thesecond PHY chip are mounted on a substrate.
 12. A physical-layer (PHY)chip, comprising: a first circuit configured to selectively operate inone of a first mode and a second mode; and a PHY circuit; and a firstphysical interface coupling the PHY chip to another PHY chip; wherein,in the first mode, the first circuit is configured to receive a firstdata stream, to obtain, from the first data stream, a second data streamassociated with the PHY chip and a third data stream associated withanother PHY chip, to output the second data stream to the PHY circuit,and to output the third data stream to another PHY chip via the firstphysical interface, and, in the second mode, the first circuit isconfigured to pass the first data stream to the PHY circuit.
 13. The PHYchip of claim 12, wherein the PHY circuit is configured to convert thefirst data stream received from the first circuit into a physical-layerdata signal for transmission on an Ethernet cable.
 14. The PHY chip ofclaim 12, wherein the first data stream is received via a high-speedphysical interface, and the first physical interface comprises alow-speed physical interface that provides a lower rate datatransmission than the high-speed physical interface.
 15. The PHY chip ofclaim 12, wherein the first circuit comprises a multiplexer that isconfigured to demultiplex the first data stream by de-interleaving bytesor bits in the first data stream.
 16. A multi-chip module, comprising: afirst physical-layer (PHY) chip, the first PHY chip comprising a firstcircuit and a physical-layer (PHY) circuit; a second PHY chip; and afirst low-speed physical interface coupling the first PHY chip to thesecond PHY chip; wherein the first circuit of the first PHY chip isconfigured to receive a plurality of data packets from a media accesscontrol (MAC) device via a high-speed physical interface, to route oneor more of the plurality of data packets having a first address to thePHY circuit, and to route one or more of the plurality of data packetshaving a second address to the second PHY chip via the first low-speedphysical interface.
 17. The multi-chip module of claim 16, wherein thefirst PHY chip and the second PHY chip are mounted on a substrate, thefirst circuit comprises a first router.
 18. The multi-chip module ofclaim 17, further comprising: a third PHY chip mounted on the substrate;a fourth PHY chip mounted on the substrate; a second low-speed physicalinterface coupling the first PHY chip to the third PHY chip; and a thirdlow-speed physical interface coupling the first PHY chip to the fourthPHY chip; wherein the router of the first PHY chip is further configuredto route one or more of the plurality of data packets having a thirdaddress to the third PHY chip via the second low-speed physicalinterface, and to route one or more of the plurality of data packetshaving a fourth address to the fourth PHY chip via the third low-speedphysical interface.
 19. The multi-chip module of claim 18, wherein theplurality of data packets are received from the MAC device via thehigh-speed physical interface at a first data rate and the one or moreof the plurality of data packets having the second address are routed tothe second PHY chip via the first low-speed interface at a second datarate that is lower than the first data rate.
 20. The multi-chip moduleof claim 16, wherein the second PHY chip comprises a second router and asecond PHY circuit, and wherein the second router is configured toselectively operate in one of a first mode and a second mode, in thefirst mode, the second router is configured to route data packets basedon addresses of the data packets, in the second mode, the second routeris configured to pass data packets received from the first PHY chip viathe first low-speed physical interface to the second PHY circuit withoutlooking at addresses in the data packets, and the second router isprogrammed to operate in the second mode.